Sixteen animals of 124 kg initial LW were used in Experiment 2 and only
treatments C and G were evaluated. The pasture used was star grass (6.0-7.1 % N x 6.25)
with rotational grazing.

The Gliricidia trees used were two years old and the main stem was cut
at 50 cm above soil level. LW gains were 0.42, 0.52 and 0.62 kg/day in treatments 0, G and
C of Experiment 1 and 0.21 and 0.32 kg/day in treatments 0 and G of Experiment 2. The LW
gain increments of 100-110 g/day obtained with restricted gliricidia grazing are similar
to the responses obtained with 0.5 kg/day of a concentrate supplement.

Gliricidia sepium foliage is a valuable feed resource for improving
live weight (LW) gain of cattle on basal diets of grasses. LW gain increments of 100 to
200 g/day have been obtained offering the harvested foliage to growing cattle in
confinement (Preston and Leng 1987; Seijas et al 1994; Zamora et al 1994),
but the "cut and carry" management involved is a limitation to its use at farm
level. An alternative to solve this problem could be direct harvesting by the animal
managed by restricted grazing of "protein" banks of gliricidia.

Two feeding trials were carried out to evaluate the influence of
restricted grazing of Gliricidia on the LW gain of growing cattle on star grass (Cynodon
nlemfuensis) pastures.

Materials and methods

Location

Both trials were carried out at the Faculty of Agronomy in Maracay,
which has a range in monthly average temperatures from 23.4 to 26.5 ºC and a mean
rainfall of 989 mm. The first experiment started in July 1994, during the peak of the
rainy season, and the second trial was conducted on the same paddocks beginning in October
of the same year, at the end of the rainy season.

Animals and design

Experiment 1:

A completely randomized design was used to compare three treatments,
(O) a control group grazing star grass, (G) sames as the control but with restricted
grazing Gliricidia during 2hours/day and (C) same as control but with 1 kg/day of
concentrate.

Eighteen Holstein x Brahman weaned cattle of 176 kg initial LW were
balanced between treatments according to LW and the duration of the experiment was 12
weeks. All animals grazed together in five 3.68 ha paddocks of star grass and received ad
libitum a mineral mixture in the field. The paddocks had occupation and rest periods
of 10 and 40 days. At 6:30 hours the animals receiving concentrate were taken out of the
field for two hours and put in individual stalls where the concentrate was offered. This
supplement contained 48.75% rice polishing, 48.75% soya bean husks and 2.50 % mineral
mixture.

The animals on the gliricidia treatment were introduced from 6:30 to
8:30 h into a paddock which had a pure stand of this tree. Five 0.2 ha paddocks were used
with occupation and rest periods of 10 and 40 days. The trees had been were established at
1 x 2 m distances, were approximately 2 years old when grazing started and after each
grazing were cut at 50 cm above soil level.

Experiment 2

Sixteen weaned Holstein x Brahman cattle, eight of each sex, were used
in a completely randomized design with a 2 x 2 factorial arrangement to compare the
restricted grazing of Gliricidia (G) with a control group grazing only star grass (0). The
same paddocks and rotations of star grass and Gliricidia of Experiment 1 were used, but
the rotations of the grass and the legume were simultaneous and the animals on Treatment G
remained continuously on the Gliricidia during the first two days and from 6:30 to 8:30 h
the other eight days. The star grass paddocks, but not the Gliricidia banks, were
irrigated when it was required. The animals in this trial had an average initial LW of 124
kg and were balanced between treatments according to weight. The duration of the
experiment was 12 weeks. All animals received a mineral mixture ad libitum in the
field.

Measurements

The animals were weighed weekly at 06:00 hours and LW gain was
calculated by the regression of LW on time. The amount of star grass on offer was
estimated by throwing 1.0 x 0.5 m quadrants six times just before and after grazing each
paddock and cutting the herbage at ground level. The samples were weighed and mixed to
obtain two sub samples, one to determine dry matter and the other to determine the
proportion of leaves, stems and dead material. Twelve Gliricidia plants of each paddock
were sampled before and after grazing by harvesting the branches from which the leaves and
woody stems were separated and weighed. The samples of herbage and concentrate were dried
at 65 ºC for 48 hours.

Average N x 6.25 content (DM basis) of whole grass samples taken at
ground level were 6.0 and 7.1% in the two experiments and increased to over 10 % in leaves
(Table 1). The NDF levels were above 75% in all grass analyses with little difference
between leaves and total biomass. The offer of standing grass before grazing was between
4,842 and 6,412 kg DM/ha in both trials and after grazing had fallen to 2956 kg/ha (Table
2). The proportion of stems was about 50 % before grazing and leaves constituted less than
30% of total DM available (Table 3). Leaf percentages appreciably decreased at the end of
the grazing periods.

Table 1: Chemical composition of the
feeds

N x 6.25

NDF

Ash

Ca

P

---------------
% of DM--------------

Experiment 1

Star grass

Whole sample

6.0

80.5

8.8

0.32

0.41

Leaves

11.6

75.2

9.2

0.38

0.49

Gliricidia

23.5

43.3

11.8

1.28

0.38

Concentrate

16.6

58.9

9.8

1.19

0.30

Experiment 2

Star grass

Whole sample

7.1

79.0

9.3

0.31

0.40

Leaves

11.4

76.4

10.4

0.50

0.46

Gliricidia

18.9

55.1

9.9

1.77

0.31

Table 2: Weight of standing forage
before and after grazing

Grass

Gliricidia

--kg DM/ha--

Experiment 1

Before grazing

4842

1037

After grazing

2956

677

Experiment 2

Before grazing

6412

617

After grazing

5204

371

Table 3: Composition of forage samples

Grass

Gliricidia

leaf:stem:other*

leaf:woody stems

Experiment 1

Before grazing

18:53:29

73:27

After grazing

7:59:34

39:61

Experiment 2

Before grazing

28:48:24

56:44

After grazing

14:57:29

16:84

The means for N x 6.25 content (DM basis) of Gliricidia foliage were
23.5 and 18.9% in Experiments 1 and 2. NDF levels were lower and calcium percentages
higher than those observed in star grass (Table 1). The offer level of Gliricidia branches
per unit area was higher in the first trial and in both experiments had a high proportion
of leaves (Tables 2 and 3). The amount of DM per ha and the proportion of leaves were
markedly reduced after grazing.

LW gains were higher in the first trial. The animals on star grass
alone (Treatment 0) gained 0.42 kg/day and LW gain increased to 0.52 and 0.62 kg/day in
treatments G and C (Table 4). LW gains also increased in Experiment 2 from 0.21 kg/day for
animals in treatment 0, to 0.32 kg/day on restricted grazing of Gliricidia.

The pastures used in both trials were high in fibre and low in N x
6.25; there were large differences in N x 6.25 content between leaves and the whole
standing biomass. The proportion of leaves in the herbage was low (Table 3), but the
animals selected this fraction and it decreased from 18 to 7 % in Experiment 1 and from 28
to 14 % in Experiment 2. The high offer level of standing biomass before and after grazing
in these trials (Table 2) and the spatial distribution of this stoloniferous grass allowed
a high degree of selection by the animals. The offer level of the standing biomass was
over 2000 kg DM/ha and no restrictions in herbage intake by this factor were to be
expected (Minson 1990).

The LW gains recorded when animals grazed star grass alone (0.42 and
0.21 kg/day in Experiments 1 and 2) were within the range of values obtained with
cultivated pastures in the tropics (Stobbs 1976). The higher values in Experiment 1 are
not explained by the chemical composition of the pastures, which was very similar in both
trials (Table 1), or by the herbage on offer which was slightly higher in Experiment 2
(Table 2). The lower LW gains in the latter trial could be related to the stress caused by
weaning the animals just before the beginning of the experimental period.

The opportunity to browse the Gliricidia trees resulted in average
increases of 100-110 g/day in LW gains. These responses are in the lower range of those
found with stall fed animals supplemented with harvested gliricidia foliage (Preston and
Leng 1987; Seijas et al 1994; Zamora et al 1994), but labour requirements
are larger with the latter management. Neither the amount of legume consumed nor its
proportion in the whole diet could be estimated in these trials. But the relatively low
offer level and utilisation (Table 2) indicate that it was only a small component of the
diet.

Supplementation with 1 kg/day of concentrate in Experiment 1 increased
LW gain by 200 g/day, which is similar to the response observed in other trials carried
out at this Institute (Combellas 1993). The responses observed with restricted grazing of
Gliricidia, of about 100 g/day LW gain, are comparable to those likely to be obtained with
a supplementation of 0.5 kg/day of concentrate.

The restricted daily grazing of Gliricidia sepium is a simple
and economical management practice, and the results obtained in these trials have shown
that moderate LW gain increases could be obtained with animals grazing cultivated tropical
grasses.

Acknowledgements

This research was partially sponsored by the International Atomic
Energy Agency, Project VEN/5/017.

References

AOAC 1984

Official Methods of Analysis (14 ed). Association of
Official Agricultural Chemists: Washington.